PROBLEM TO BE SOLVED: To provide a method for immunostimulation of fish and shellfish, which simply and inexpensively activates immunological effect of fish and shellfish.SOLUTION: The method for immunostimulation of fish and shellfish includes administering a yeast extract having &ge；20 mass% content of 5'-nucleotides and &ge；10 mass% content of a free amino acid to fish or feeding a feed mixed with the yeast extract to fish and shellfish. The method for raising fish and shellfish is provided.【課題】簡便且つ安価に、魚介類の免疫作用を賦活することができる魚介類の免疫賦活方法の提供。【解決手段】５’－ヌクレオチド類の含有量が２０質量％以上であり、且つ遊離アミノ酸の含有量が１０質量％以上である酵母エキスを投与する、または該酵母エキス配合の飼料を摂餌させることを特徴とする、魚介類の免疫賦活方法及び、魚介類の飼育方法。【選択図】図１
